doc: Move license file to docs folder

As in TF-A, the license file can be included in the rendered
output by moving it into the /docs folder.

Change-Id: I0a7b9c410f6567c260cb4701148955e1273e8285
Signed-off-by: Paul Beesley <paul.beesley@arm.com>
diff --git a/docs/index.rst b/docs/index.rst
index 8a32608..29b25d5 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -11,6 +11,7 @@
    implementing-tests
    design
    change-log
+   license
 
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